The present invention relates generally to emulsion coating compositions and specifically to a high gloss, sag resistant solvent resin paint or varnish having water dispersed therein.
It has heretofore been difficult to provide quick drying water-in-oil emulsion solvent resin compositions which yield a high gloss coating. These compositions include water as part of the evaporative vehicle and comprise a dispersion, through the use of suitable emulsifiers, of up to 80% by weight of water in a solution of organic solvents and a solvent soluble film-forming resin. The substitution of a large portion of dispersed water for part of the evaporative vehicle in such compositions is not without problems where a high gloss, quick setting coating is desired.
In order to provide a paint or varnish that may be used on a non-horizontal surface, it is imperative that the composition set or thicken quickly to avoid the rippled surface which will result from the sagging or flowing of the coating. However, the use of only low boiling point solvents to accomplish this end has invariably resulted in a dull or hazy finish on the workpiece. In addition, the dispersed water may coalesce into larger droplets which, upon evaporation, leave unsightly blemishes on the film surface.
Thus, it has been impossible to compound a water-in-oil solvent resin coating emulsion which will afford the quick set necessary for sag resistance as well as a smooth, high gloss finish. These qualities are important in all finishes, but are especially desired in compositions to be dispensed from pressurized containers, commonly known as aerosol spray finishes.
These problems result from the inclusion of water as the dispersed phase of the emulsion. Standard non-emulsion aerosol or quick setting paint has a high percentage of low boiling point solvents i.e. 70% to 80% by weight of the solvent having a boiling point of from 100.degree. to 200.degree. F. This allows a quick set of the finish. When a high percentage of low boiling solvents is used in a water-in-oil emulsion composition, the water does not evaporate before the film closes and is trapped, in microscopic droplets, within the coating.
This contributes to a dull finish in several ways. First, the trapped bulk water causes precipitation of insoluble resin compounds which forms a haze in clear coatings. Also, a uniform dull finish will be formed if the water droplets penetrate the partially set film to evaporate and the coating lacks the resiliency to close the resultant surface imperfections. In addition, thicker film coatings, such as occur at the edge of sprayed workpieces, produce wide variations in gloss due to the increased time required for the evaporation of the water from those areas.
Also, the dispersed water droplets may tend to coalesce to form larger droplets which, while not noticeably affecting a non-gloss coating, cause unsightly blemishes and otherwise affect the gloss of the paint or varnish.
As used herein, the term quick setting defines a rapid partial formation or thickening of the film which is sufficient to arrest flowing or sagging of the newly applied coating. Quick drying relates to the time necessary to produce a tack free film on a substrate. The compositions of the present invention may have varying drying or curing rates dependent on the resins employed. Generally, a paint or varnish composition having a setting time in excess of five minutes will have a marked tendency to flow and sag.